Ion implanters are applied widely in manufacturing semiconductor wafers. Before an ion beam is implanted, the angle between the normal axis of the surface of wafer 416 and the direction of the ion beam 404 (as shown in FIG. 1), named implant angle, is adjusted to a desired value. The wafer 416 is fixed on the wafer holder 414. When the ion beam is implanted, the wafer holder 414 is then driven to bring the wafer to perform repeatedly translational scan perpendicular to the direction of ion beam implantation, while maintaining implant angle unvaried. To ensure the dose of ion implantation over the wafer to be uniform, it's necessary to precisely control the implant angle and the scanning motion of the wafer holder 416.
In conventional ion implanters as shown in FIG. 1, a scanning mechanism with a wafer holder 414 which utilizes serial kinematic mechanism is installed in champer 700 (for example, as illustrated in International Publication No. WO02/43104 entitled “Hybrid scanning system and methods for ion Implantation” filed by Varian Semiconductor Equipment Associates, Inc. on May 30, 2002). In the so-called serial kinematic mechanism, there is provided only one kinematic chain from the wafer holder 414 to the location where the scanning mechanism is fixed to the wall 28 of ion implant chamber 700. In ion implant chamber 700 shown in FIG. 1, knuckle 604 is driven by motor 1 (not shown) to be rotatable around an axis 605, so as to adjust the implant angle at which ion beam 404 impinges on surface 418 of wafer 416. Meanwhile, wafer 416 together with wafer holder 414 and the like are driven by motor 2 to perform repeatedly translational scan along direction Y in the figure.
The above serial kinematic mechanism is fixed on wall 28 of the ion implant chamber by its fixing link. Motor 2 is installed outside the ion implant chamber and motor 1 that drives the wafer holder to rotate is arranged inside the ion implant chamber to be coupled with mechanism 604. The weight of motor 1, which is relatively large and increases the load of the scanning mechanism, leads to rise in the power consumption of motor 2 and being prone to cause the above serial scanning mechanism bent and distorted, thereby exacerbating error in angle control and scan control of the wafer.